1. Field of the Invention
The present invention relates to an information recording/reproducing apparatus, and more particularly to a fuzzy controller for an actuator and the controlling method thereof in an information recording/reproducing apparatus.
2. Description of the Prior Art
Recently, the information recording/reproducing apparatus, which records and reproduces information on and from a mass information storage media, is gradually being enhanced in its precision and functions with advanced design techniques.
The information recording/reproducing apparatus forms tracks on the information storage media to record information thereon or to reproduce information therefrom. The information recording/reproducing apparatus moves an actuator to a target track on which information is to be recorded or from which information is to be reproduced (track seeking operation). Further, when the actuator reaches the target track, the information recording/reproducing apparatus controls the actuator to follow the target track exactly (track following operation).
Moreover, techniques employing a fuzzy inference unit have been disclosed for controlled the track seeking and track following operations.
FIG. 1 is a block diagram for showing a conventional fuzzy controller using a fuzzy inference unit in a feedback system. The conventional fuzzy controller of FIG. 1 is disclosed in U.S. Pat. No. 5,251,124 granted to Nobutomo Matsunaga. As shown in FIG. 1, a first error generator 10 generates a first error value e based on a difference between a present feedback value Y from an actuator 8 and a desired value r from a reference data generator 9. First error value e is applied to a desired value correction unit 11. Desired value correction unit 11 generates a corrected desired value r, which is inputted to a second error generator 12, by applying predetermined correction constants K.sub.p and K.sub.i to first error value e in accordance with the following formula: EQU r=r+K.sub.p *e+K.sub.i .intg.e dt, wherein e=r-Y.
Second error generator 12 generates a second error value em based on a difference between present feedback Y and corrected desired value r. Second error value em is applied to a differentiator circuit 13 and a fuzzy inference unit 14. Fuzzy inference unit 14 generates a control signal S based on fuzzy rules and membership function in accordance with second error value em and differentiated second error value .DELTA.em from differentiator circuit 13.
As can be seen in the above formula, whenever an error e (=r-Y) remains, the value of K.sub.1 .intg.e dt will be increased and thus corrected desired value r will also be increased to become larger than desired value r. Accordingly, second error value em from second error generator 12 becomes larger than first error value e. Inputs of these two larger values em and .DELTA.em to fuzzy inference unit 14 for fuzzy inference enable the fuzzy controller to output a larger value for control signal S. Therefore, actuator 8 can be controlled since control signal S has a larger value even though the fuzzy controller generates a small error value in its steady-state track following operation.
However, the fuzzy controller has a drawback in that overshooting at a target track can be easily generated in a track seeking operation since a larger corrected desired value than a desired value is used for controlling the actuator.
FIG. 2 is a block diagram for showing another conventional fuzzy controller using a fuzzy inference calculation circuit in a feedback system. The conventional fuzzy controller of FIG. 2 is disclosed in U.S. Pat. No. 5,267,144 granted to Shuich Yoshida et al. As shown in FIG. 2, an actuator 227 is moved by a driving unit 230 when an access command signal P is applied to a fuzzy controller 221. A position of actuator 227, which generates a position signal X, is detected by a position encoder 228 and a position detection circuit 229. Position signal X is inputted to a velocity detection circuit 210 from which a velocity signal V of actuator 227 is generated. Fuzzy controller 221 has a fuzzy inference unit 222, a microcomputer 223, a memory 224, an interface circuit 225 and a driving signal generator circuit 220. Driving signal generator circuit 220 corrects the data of access command signal P based on a correction value obtained by fuzzy inference unit 222, and outputs a driving signal U including corrected data of an acceleration, an acceleration time, a deceleration and a deceleration time of actuator 227 to a driving circuit 226. Accordingly, a driving output current I, which is generated from driving circuit 226 when driving signal is inputted thereto, is applied to actuator 227.
FIG. 3 is a graph for showing the unevenness of a force for moving an actuator in accordance with positions of the actuator in a conventional feedback system. As shown in FIG. 3, a force is applied to actuator 227 uniformly when actuator 227 lies in a range between a position X.sub.u1 and a position X.sub.u2 on a disc, but not uniformly applied to actuator 227 when actuator 227 is beyond the range. Fuzzy controller 221 moves actuator 227 by distance X.sub.d to obtain an acceleration time T in the range of even force, X.sub.u1 &lt;X.sub.e &lt;X.sub.u2. Acceleration time T is stored in memory 224 and referred to when necessary. When a starting position X.sub.s of actuator 227 is in the range of even force, X.sub.u1 &lt;X.sub.e &lt;X.sub.u2, actuator 227 is accelerated during the acceleration time T for a target track. After the time T, actuator is decelerated and stops at a certain position. When starting position X.sub.s of actuator 227 is in the ranges of uneven force, X.sub.s &lt;X.sub.u1 or X.sub.s &gt;X.sub.u2, acceleration time T can not be used for accelerating actuator 227 for the target track and making a velocity of actuator 227 zero at the target track. Therefore, a correction time .DELTA.T for correcting acceleration time T is calculated by a fuzzy inference in accordance with the following formula to obtain a corrected acceleration time T1: EQU T1=T+.DELTA.T
That is, fuzzy controller 221 controls a track seeking operation of actuator 227 by correcting acceleration time T according to staring position X.sub.s. However, a correction of acceleration time for an actuator disables an actuator to reach a target track without overshooting at the target track.